Microsoft's provided a preview of Longhorn at WinHEC 2004. The upcoming operating system revision from Microsoft will feature a new user interface called Avalon which will a more colorful 3d interface, which apparently bears a resemblance to Mac OS X according to the author.
A full beta is not expected until 2005, and the average system requirements are expected to be a 4-6GHz PC with 2GB of RAM and one terabyte of storage.
This early preview is to be distributed to developers at the end of the WinHEC conference so more information will likely become available of this conference.